Electrocatalytic Mechanisms in Hydrogen and Oxygen Evolution Reactions

Electrocatalytic water splitting comprises two half-reactions: the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER). Both processes proceed via proton-coupled electron transfer steps at the catalyst–electrolyte interface and are governed by the binding strengths of reactive intermediates, as visualised in volcano-type activity plots. In HER, optimised binding of adsorbed hydrogen atoms (*H) minimises the barrier to H–H bond formation, whereas in OER the formation and coupling of oxygen intermediates (*OH, *O, *OOH) dictate overall kinetics. Surface structure, electronic configuration and dynamic restructuring under operating conditions all influence active-site density and intrinsic turnover frequency. Advances in operando spectroscopy, theoretical modelling and interface engineering are converging to accelerate catalyst design for efficient, scalable hydrogen production in both acidic and alkaline media.

Research from Nature Portfolio

Recent studies have elucidated the microscopic origins of activity in iridium-based catalysts for the oxygen evolution reaction. Operando optical spectroscopy investigations of amorphous IrOx and crystalline IrO2 have quantified the density and energetic landscape of redox-active centres, revealing that repulsive interactions among adsorbed oxygen species weaken *O binding at high coverages and accelerate O–O bond formation. A modified volcano plot has been proposed to guide the optimisation of intrinsic water-oxidation kinetics by tuning binding energies and adsorbate interactions. In hydrogen evolution, one-dimensional platinum–nickel/nickel sulfide heterostructures with abundant interfaces have demonstrated synergistic enhancement of alkaline HER, achieving current densities nearly ten-fold higher than commercial Pt/C at low overpotentials through interface engineering. Furthermore, single-atom ruthenium catalysts anchored on nitrogen-doped carbon supports have emerged as highly active and stable OER electrocatalysts in acidic media, where dynamic adsorption studies have identified the pivotal role of isolated oxygen atoms on Ru sites under operating potentials, driving both activity and durability.

Electrocatalytic Mechanisms in Hydrogen and Oxygen Evolution Reactions publication trend

The graph below shows the total number of articles in electrocatalytic mechanisms in hydrogen and oxygen evolution reactions across all publications each year (not limited to Nature Index journals).

Technical terms

Overpotential: The additional potential required beyond the thermodynamic equilibrium to drive an electrochemical reaction at a given rate.

Active-site density: The number of catalytically active centres per unit area or mass that participate in the reaction.

Adsorbate–adsorbate interaction: The energetic interaction between neighbouring adsorbed species on a catalyst surface, influencing binding strengths and reaction rates.

Turnover frequency (TOF): The number of reactant molecules converted to product per active site per unit time, reflecting intrinsic catalyst activity.

Superoxo species: A surface intermediate featuring an O2– moiety bound to a metal centre, often implicated in oxygen evolution mechanisms.

References

1. Unravelling the effects of active site density and energetics on the water oxidation activity of iridium oxides. Nature Catalysis (2024).
2. Precise tuning in platinum-nickel/nickel sulfide interface nanowires for synergistic hydrogen evolution catalysis. Nature Communications (2017).
3. Dynamic oxygen adsorption on single-atomic Ruthenium catalyst with high performance for acidic oxygen evolution reaction. Nature Communications (2019).
4. Deciphering Water Oxidation Catalysts: The Dominant Role of Surface Chemistry over Reconstruction Degree in Activity Promotion. Nano-Micro Letters (2024).
5. The importance of nickel oxyhydroxide deprotonation on its activity towards electrochemical water oxidation. Chemical Science (2016).
6. “The Fe Effect”: A review unveiling the critical roles of Fe in enhancing OER activity of Ni and Co based catalysts. Nano Energy (2021).